ESDU 95025

Drag due to lift for plane swept wings, alone or in combination with a body, up to high angles of attack at subsonic speeds.

ESDU 95025 applies to wings of straight taper with transition near the leading edge. It uses a semi-empirical correlation to derive the attainable leading-edge suction from the theoretical leading-edge suction on a thin wing presented in ESDU 94037 which models the variation of drag due to lift between the limits appropriate to inviscid attached flow and to fully-separated flow. The resolved components of wing viscous axial force and of body axial force and normal force provide additional contributions to total drag. The variation of wing lift with angle of attack is predicted using the leading-edge suction analogy. That lift prediction includes the non-linear contribution from leading-edge vortex flow that is present for highly-swept wings, together with a side-edge vortex contribution, but the method is limited to angles of attack where the full realisation of the predicted potential flow contribution is not degraded by flow separation over the main part of the wing. For the body normal force contributions to lift and drag, ESDU 90034 may be used if the body can be approximated by an axisymmetric shape. The contributions of the various terms are illustrated and comparisons are made with experimental results for a number of cases and suggest the method yields drag coefficient to within 0.01 of lift coefficient up to 70 per cent of maximum lift for wings with leading-edge sweep exceeding about 15 degrees.